Transmission circuits



Patented May 27, 1924.

, UNIT-Eo fsTATlzsfv l V1.495.422 PATENT OFFICE.

` ROBERT c. marinas, OF NEW YORK, N. Y., AssIoNon. TOwns'rEnN memo com- PANY, INCORPORATED, F YORK, vN. Y., A CORPORATION OF NEW YORK.

TRANSMISSION cnicurrs,

applicati@ med July 15, 1921. serial No. 484,896.

To all whom z't may concern.'

Be it known that I, ROBERT C. MATHEs,

a citizenof the United States, residing at New York, in the county of Bronx, State of 6 New York, have invented certain new and useful Improvements in Transmission Cir'- cuits, of which the following is av full, clear,

concise, and exact description.

' This invention relates to transmission ciri l cuits employing amplifiers or repeaters, and` more particularly it relates to varyingv or adjusting the gain of the circuit. V

Oneof the objects of the invention is to vary the voltage impressed upon the amplifying element while maintaining fixedi the impedance of the gain adjusting means and the element as seen from the incoming. line. 4A further. object is to provide suchfa gain I adjusting coupling circuit for a repeater to its incomin line that the impedance offered by the coup ing circuit'is independent of the frequency over a considerable range, so that uniform transmission of a band of frequencies sucl as those composing speech is se- 2cured -In accordance with this invention, the preferred form of this coupling ycircuit com prises a transformer, which is usually of the step-up type, having its primary side 3 shunted by an artificial line such as a resistance, of a value' preferably equal to thel impedance of the incoming line and; arranged symmetrically with respect to both the incoming line and the primary winding. The effective secondary voltage ofthe transformer which is impressed uponthe amplier may be varied by transformer taps to -the secondary winding, for example. lThis invention will be better understood' by reference tothe following detailed description 'taken' in connectionywith the accompanying drawing, vwhich represents the preferred form of this invention embodied in a. 21 repeater circuit.

The drawing disclosestwo physical circuits and the derived phantom circuit of a signaling system rovided with repeaters of the 21 type w ich have gain adjusting means of the type preferred by this invention. One of the physical circuits comprises a line section 10, 11, and a second line section 12, 13. A 21 type repeater circuit for these two line sections is provided by` taking off connections 15 and 16 from the midpoims of the* line windings- Of the threewinding transformer 14 to the input te1. minals of a vacuum tube am lilier 17the output `terminals of the ampli er being connected to the third winding 18 ofthe threewinding transformer 14. Asis wellknown inthe art, such anv arrangement provides Afor the amplification ofI signals from either;

line section 10, 11, orline section 12,'13, the

incoming' weak signals being impressed across the midpoints of the line windings of the three-winding transformer upon the input circuit of thel amplier, `thereby being amplified and impressed bywinding 18 upon both line sections'10,l11 and 12, 13.' Line section 10, 11 vof course should) present the same impedance'as line section 12, 13, in

order to prevent repeater 17vfrom singing.

Inasmuch as it is frequently desirable to Vary the effective amplification or'gan of 4repeater- 17 to meet conditions in line sections 10,'11I and 12, 13, and particularlyto adjust repeater 17 so that it may be employed for repeating betweenv a plurality of line secton's'"requir1ng different degrees of, amplification, the repeater 17 isf provided with the gain adjustin -means of this invention. This gain adjusting means for coupling repeater 17 to the midpoints of the vline windings of the three-winding transformer.14 comprises an input transformer 20, preferably of the step-up type, which has itsV primary winding 21 shunted'b aV fixed resistance 22. The secondary win 'ng 26` is provided vwith a plurality of taps 23, t0 any 24 of the repeatermay bel connected-by a movable arm 25. It .is obvious from lthe drawing thatwhen arm 25 ismovedI lin either direction, a variation takes place in the amount of input potential impressed upon the repeater 17 so that the variation of the position'of arm 25 serves to controlthe in- 'tensity of the amplified currents in thel Outloo' put circuit ofthe repeater.

' As v previously stated, transformer 20 should preferably be of the step-up type, and in particular it mill be found preferable to one of whichthe control electrode,

employ a transformer having an impedance ratio of about 1:600. The resistance 22 should preferably have such a value asv to equal the combined impedance of .line sec-4 tions 10, 11 and 12, 13, as seen from the in ut connections 15 and 16. Since two e sections as seen from connections 15 and 16 are connected in parallel it follows that resistance 22 should have a value equal to onehalf the impedance of one of the line sections 10, 11 or 12, 13. Due to the fact that the impedance between the input terminals of the repeater 17 is of a high order of magnitude, it follows that the impedance of the secondary winding as seen from connections 15 and 16 is practically the same as if the secondary winding were open-circuited. Any variation, therefore, in the position of arm 25 will not aect appreciably the impedance of the gain adjusting means and the repeater as seen from the connections 15 and 16.- rll`he coupling means of this invention therefore presents a nearly fixed impedance to the incomingr line, so that the impedance relations therebetween are unaffected by adjustments that are made to vary the voltage impressed upon the amplifier. Due to the uniform impedance relations previously specified, this coupling circuit just described also enables repeater 17 to give a uniform transmission of' a band of frequencies such as those composing speech.

The other physical circuit shown in the drawing comprises two line sections 30, 31 and 32, 33. 'lhe repeater element 34 for these two line sections is connected thereto in a similar manner as previously described for repeater 17. rll`he gain of repeater 34 may be varied by movinigarm 35 to a desired tap of the secondary winding of the step-up input transformer 36.

A. 21 repeater for the phantom circuit derived from line sections 10 to 13 and 30 to 33 is provided by input connections 38 and 39 connected respectively to the midpoints of the primary windings of transformers 20 and 36. r1`hese connections 38 and 39 lead to an input transformer 40, the secondary winding of which is connected to the input circuit of a repeating element 41. The output circuit of repeater 41 is connected to an output transformer the primary windings of which are 42 and 43, and the secondary windings of which are located in the four line sections and comprise windings 44 to 51 inclusive. This arrangement for obtaining input-and output connections for a phantom circuit is not a part of this invention, but is described and claimed in an application to Blackwell, Serial No. 300,556, filed May 29, 1919. rlfhe gain of phantom repeater 41 may be adjusted by selecting a desired tap on the secondary winding of the input transformer 40.

@ne of the advantages of the coupling means of this invention is that when the phantom tap is taken as shown from the midpoint of the primary winding of the input transformer for the physical circuit repeater, the gain of the phantom repeater may be adjusted independently of the gain of the hysical circ :it repeater and vice versa. gaince Lacasse there are no variable connections between leads 15y and 16 and primary winding 21, which is fixed, it follows that a variation in the position of arm 25 to vary the gain of repeater 24 will not affect the phantom currents flowing in parallel through connections 15 and 16 and connection 38 to the input transformer 40. 1t will be similarly apparent that a variation in the gain of repeater 41 will not affect the physical circuit currents flowing serially through connections 15 and 16.

llt is to be noted that the input connections to the primary winding of the input transformer are not shown connected to the outside terminals of the primary winding, but are shown connected to intermediate points. llhis is to indicate that, if desired, the effective number of turns of the primary winding may be varied to vary the impressed voltage upon the repeater, or they may be set at the factory or by the installer to correspond to given circuit conditions. ltn this way a standard transformer becomes somewhat flexible and answers for various line requirements. rll`his is particularly true in case it is not desired to obtain the phantom tap from the midpoint of the primary winding of the input transformer, for then the repeater gain may be adjusted by a variation in the effective number of turns of the primary winding without producing the interference mentioned above between the side circuits and the derived phantom circuit.

lnput couplings for repeaters areknown in which the secondary of the transformer is shunted by a high resistance having a potentiometer tap for taking o voltage, but the coupling 0f the present invention has considerable advantages over types heretofore known in that it is more economical to construct and more convenient to operate in practice. By having the balancing resistance across the primary winding, for example, thc transformer carries less current than if the resistance is across the secondary, and the transformer coils can therefore be made of smaller gauge wire without excessive transmission losses. A smaller resistance also is required. Furthermore, where several repeaters `are associated together in small space, as is usual in actual practice, there is less liability of crosstalk if the balancing resistances and their windings are located in the primary or low voltage side of a transformer rather than in the high voltage side.

llt will be apparent to those skilled in the art that the specific embodiments of the invention described above may be variously modified without departing in any wise from the spirit of this invention as defined in the appended claims. While the invention has been described above in connection with a telephone repeater circuit of the so- VLaing-ias:

called 21 type, it is obvious that the'gain adjusting means of this invention is applicable to other types of telephone or other signaling circuits,vsuch as the 22 repeater type or four-wire circuit type.

'hat is claimed is:

1. The combination of an incoming line, a telephone repeater, and means having-a substantially uniform transmission efficiency throughout a wide range ofV frequencies for coupling said repeater to said line, said coupling comprisingI a transformer between said repeater and said vline, a resistance'in shunt to said line, and adjustable terminals to various ploints Qn a winding ofV said-f' transformer" for varying the .transformer 4' 'secondary voltage vwhile maintaining the amount of resistance included in said line substantially constant.

2. In combination, a signaling line, .a re-i peater for repeating signals from said line, and a repeater gain ad]usting meansvcomprising a transformer having a windin in.

circuit with said line and a second win ing in circuit with said repeater, one of`said windings having a plurality of taps ar- 'anged between its extreme terminals and a vmovable member cooperating with Said taps to vary the effect-ive valve of said winding included in circuit with said'line and repeaten In combination, anincoming line, an outgoing line, a repeater for repeating b etween said lines, a transformer having primary and secondary windings between said.

winding said resistance having a .value suf-- cient to maintain substantially constant the impedance of said repeater as seen vfrom the line, said secondary winding having one terminal permanently connected to onev input terminal of said repeater, and any adjustable connection between another input terminal of said repeater anda point onsaid secondary winding. j v

5. In combination, .an incoming line, an outgoing line, a vacunar tube repeater therebetween, a transformer between said incoming line and said repeater and haviupr a primary and a secondary winding, and means for varying the effective number of turns of one of said windings when a fturns of the winding.' f

change., isv desiredv inthe gain' of vsaid repeater while vmaintaining balanced the two sides of said incoming line with respect to the midpoint of said primary winding'.l

(. In combinatiomarepeater,` an incoming line therefor, a coupling circuitbetween said iepeater and said line ycomprising a transformer having a primary and a secondary winding, andlneans forl making said repeater have a s ubstantiallyconstant `iinpedancefor a wide range of-frequency las seen vfrom said'-V line, one 'of said transformer windings havingl adjustable .terini-l 'l nals forv varying'-the effective vnumber of 7 In combination, a.- repeater, an incoming line, a coupling circuit between said repeater andl said line'comprising aV trans.

' former having a primary and a secondary winding, means for causing said-repeater to present a substantially constant impedance for a wide range of frequency as seen fromsaid line, and means for varying Ithe effective value of one of' said windings while maintaining substantially constant-V tlie impedance of said repeater as seen .from

lsaid line.

8. In combina-tion, a repeater, a signal? ing line, a coupling circuit between said repeater and said line comprising a transformerphaving a primary and a secondary windin a resistance in-shnntto `one of said windings having a value sutlicient .to

cause said repeater 'to presenta 'sub`stan -v i.

line, and means for varying'thefeifectiye tially constant impedance'as se'eli'-from said.

number of turns of one lof said/,windings while maintaining substantially y constantthe impedance of said repeater as seen from'- said-line. 'f f 9.v In combination, an incoming line, a phantom circuit repeater for saidline, a

fao,

physical circuit repeater v for said line, 'a

coupling circuit between said vline and 'said lphysical circuit repeater Vcomprising 4a.

transformer having al primryiwindin'g and a secondary winding, aj-phantomfta "from the midpoint of said-primarywin ingto.

ing the ain .offs'aid physical .'.circuit re,` )eater in ependently Iof 'the'jgainfdesired` by said phantom repeater, saidl means comprising ai plurality of taps fto'vsaid,v Secondary windiig A and a mova lcv-arm-l n cooperating p therewith.-

lsaid phantom repeater,.andineans vfo'r"i'7a.'1'y-j .l

170.5111 combination, -an'lincoming une, a

physical circuit repeater'for'said line, a coupling circuit between said line and Said physlphantom circuit repeater for js'aid lline, a l

icalcircuit repeater comprising a transforml er having a' primary winding and a secondary winding, an artificial line in'circuit with said primary winding for causing the pedance looking into the physical, circuit repeater to be equal to the impedance lookiosf i ing into said line, a. phantom tap from the midpoint of said primary Winding to said phantom repeater, and means for vvarying the gain of said physical circuit repeater independently of the gain desired by said phantom repeater, said means comprising -a variable connection from an input terminal of said physical repeater to a desired point on said secondary winding.

11. lin combination, a line, a repeater therefor, and means for varying the effective gain of said repeater While maintaining fixed the impedance of said repeater as seen from said line, said means comprising means for varyingr the gain of said physical 20 circuit repeater independently of the gain of said phantom repeater, said means comprising a transformer having a plurality of taps to one of its windings.

lin Witness Whereoffll hereunto subscribe 25 my name this 14th day of July A. D., 1921.

sonner c. Martins.

a plurality of taps i5 

